In slight hemolysis, which enzyme activity is most affected?

• A. LD
• B. ALT
• C. AST
• D. CK

Answer: (A)

Red blood cells contain large amounts of lactate dehydrogenase (LDH), so when a sample undergoes even mild hemolysis, LDH is released into the serum in greater quantities than most other enzymes. This makes the measured LD activity rise disproportionately in hemolyzed samples. In contrast, ALT is mainly a liver enzyme, CK is abundant in muscle and heart, and while AST is present in various tissues including RBCs, its concentration in RBCs is not as high as LDH; so hemolysis does not affect it as dramatically. Therefore, LDH is the enzyme most affected by slight hemolysis.